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The preparation of potassium iodide-starch paper is made
by clipping strips of filter paper into a thin solution of starch
paste to which a little potassium iodide has been added, and
drying the paper.
The oxidation of a side-chain by means of permanganate
solution is one which is commonly employed where the acid is
required. The monohalogen derivatives are readily oxidised in
this way, but greater difficulty is experienced if two halogen
atoms or other acid groups are present. The dichlorotoluenes,
for example, are only slowly attacked.
lodOBOtoluene. The most interesting of the compounds
belonging to this group, which were carefully investigated by
V. Meyer, is the substance prepared by shaking a mixture of
iodosoben/ene and iodoxyben/.ene (obtained by the oxidation of
the iodoso-compound) with moist silver oxide. Diphcnyl-
iodonium oxide is thus produced, which in basic properties
resembles ammonium hydrate,
c,;ii:,in j <Y,n,,i<>:. i Agon    (r(;ii;,u.oii i- Agio.,.
With hydriodic acid it forms the iodide, (C(iII,-).J.I.
Diazoaminobonzeiie. Dia/oamino-compounds are also
formed by the action of dia/.onium salts on primary and
secondary amines of both the aliphatic and aromatic series.
The method given in the preparation must then be modified.
The dia/.onium salt is first prepared, and the amine stirred in
with the addition of sodium acetate. The sodium combines
with the mineral acid, liberating the weaker acetic acid, which
thereby assists the separation of the tlia/.oainino-compound.
Compounds of the following formula; have been prepared in
this way.
(',;II ,N:N.C,}n I.CH..    I)iuy.c>l>Lmeno-:imiiioloUtenc
< %t;l I;,N:N. NHC.,1 I;,      I)i:t/,obcn/.cc-cthyl:iminc.
< Y,I I;,N:N.N(C! i:,)o       Diaxoben/cne-dimethyUimme,
I )ia/.obenzene-pipcridine.